Method of electroplating on chromium or chromium-iron alloys



Patented Dec. 13, 1949 METHOD OF ELECTROPLATING ON CHRO- MIUM OR CHROMIUM-IRON ALLOYS Eric Frederick George McGill, Twickenham, England, assignor to Electric & Musical Industries Limited, Hayes, England No Drawing. Application July 28, 1945, Serial No. 607,662. In Great Britain August 2, 1944 2 Claims. (Cl. 204-34) This invention relates to electro-plating.

In electro-plating chrome-iron alloys it is found diflicult to provide a good adherent film of plated metal on said alloy which will not blister on heating or peel off when the alloy is bent to breaking point. Accordingly, it is the object of the present invention to provide an improved method of electro-plating in particular for chrome-iron alloys with a View to avoiding these disadvantages.

According to the invention a method of electro-plating is provided in which the metal to be plated, prior to the plating operation, is provided with a thin film of sodium or potassium bisulphate. Preferably, the sodium or potassium bisulphate is applied to the article by dipping the article in a bath of molten sodium or potassium bisulphate at a temperature of about 300 to 350 C. The sodium or potassium bisulphate film thus applied serves, it is believed, to remove any resistant oxide film and to protect the articles from reoxidation, the film solidifying on the article as the film cools.

The invention is particularly applicable to the electro-plating of chromium alloys, in particular chrome-iron alloys, and in one example of the invention the articles made from such an alloy or sheets or other preformed members of such an alloy, hereinafter referred to collectively as articles, are first electrolytically cleaned or cleaned in any of the other manners known in the art and then dried. The articles are then dipped for about five seconds in a bath of fused hydrated sodium bisulphate maintained at a temperature of about 300 to 350 C. and then allowed to cool. The articles are then made the cathode in a nickel plating bath and during the electroplating action the bisulphate film is dissolved and replaced by a film of nickel. The articles are then removed from the bath, washed thoroughly and, if desired, provided with a further coating of another metal, such as copper. Where such a further coating is required, a copper cyanide plating bath is preferably employed and a desired thickness of copper is thus applied to the articles.

It is found that the bisulphate film applied to the articles protects the latter from oxidation after having been cleaned by normal methods so that platings of copper applied to articles formed of chrome-iron alloys will not blister on heating or peel off when the articles are bent to breaking point. Satisfactory results have been obtained with a chrome-iron alloy containing 23 per cent of chromium, and. with pure chromium both in the solid form and as a plating.

It may be found unnecessary, if copper plating is required, to plate the articles first with nickel since, in some cases, the articles may be plated directly with copper. Of course other plating metals can be employed instead of nickel or copper. Also the invention is not necessarily limited to the plating of articles made of chromeiron alloys.

The invention is particularly suitable for use in the plating of chrome-iron pins which are ultimately sealed to a glass .base or envelope of a high frequency electron discharge device. Such pins are preferably copper plated in order to increase their electrical conductivity.

What I claim is:

1. A method of electroplating on a basis metal consisting essentially of chromium and iron, said method comprisin cleaning and then drying said basis metal, dipping said basis metal in a bath of a fused salt from the class consisting of sodium bisulphate and potassium bisulphate, whereby said basis metal is provided with a thin film of said salt to protect the basis metal from oxidation, withdrawing the filmed metal from said bath, allowing the filmed metal to cool, and then electroplating upon said basis metal in a bath of a metal from the class consisting of nickel and copper, whereby the bisulphate is dissolved and is replaced by a coating of said last mentioned metal.

2. A method according to claim 1 in which said basis metal consists of chromium.

ERIC FREDERICK GEORGE MoGILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,306 Lukens Mar. 23, 1937 1,665,638 Morrison Apr. 10, 1928 1,726,623 Hollnagel Sept. 3, 1929 1,795,512 Schmidt Mar. 10, 1931 1,950,689 Nachtman Mar. 13, 1934 2,285,548 Wesley June 9, 1942 2,293,810 Domm Aug. 25, 1942 2,353,026 Gilbert July 4, 1944 2,419,190 Wagoner Apr. 15, 1947 2,441,776 Tainton et a1 May 18, 1948 FOREIGN PATENTS Number Country Date 527,754 Great Britain of 1940 133,813 Sweden of 1929 OTHER REFERENCES Iron and Steel, June 1944, page 501. 

